Are you getting ready for a technical interview that might involve REST API questions? You might be feeling a mix of excitement and nervousness right now. Technical interviews can be challenging, especially when they focus on specific concepts like REST APIs that are so important in modern software development.
I’ve coached hundreds of job seekers through technical interviews, and I’ve seen firsthand how proper preparation can transform anxiety into confidence. In this guide, I’ll share the most common REST API questions you’ll face and exactly how to answer them to impress your interviewer and stand out from other candidates.
REST API Interview Questions & Answers
These questions and answers will help you showcase your knowledge of REST APIs during your interview. Each question includes an explanation of why interviewers ask it and tips to craft an impressive answer.
1. What is a REST API and what are its key principles?
Interviewers ask this fundamental question to assess your basic understanding of REST architecture. They want to confirm you grasp the core concepts before diving into more complex questions. This question sets the foundation for the rest of the API discussion.
To answer effectively, start by defining REST as an architectural style for designing networked applications, then explain its key constraints. Focus on how these principles make REST APIs scalable and flexible, which are qualities companies value in their systems.
Most importantly, demonstrate your practical understanding by briefly explaining how these principles affect real-world API design. This shows you can apply theoretical knowledge to actual development tasks.
Sample Answer: REST stands for Representational State Transfer, which is an architectural style for creating web services. The key principles include a client-server architecture, statelessness (the server doesn’t store client context between requests), cacheability, a uniform interface using standard HTTP methods, and a layered system that organizes each type of server. These principles make REST APIs simple to use yet powerful enough for most applications. In my experience, following these constraints leads to scalable, maintainable systems that are easier for other developers to understand and use.
2. How does REST differ from SOAP?
Interviewers ask this comparison question to check if you understand different web service approaches. They want to see if you can articulate the trade-offs between technologies, which suggests deeper knowledge than just familiarity with one approach.
When answering, highlight the key structural and philosophical differences between REST and SOAP. Explain how REST’s simplicity contrasts with SOAP’s strict standards and why one might be chosen over the other in different situations.
For an impressive answer, include a brief mention of when you might recommend each approach based on project requirements. This demonstrates practical judgment beyond theoretical knowledge.
Sample Answer: While REST is an architectural style with flexible implementation, SOAP is a more rigid protocol with specific requirements. REST uses standard HTTP methods and typically returns data in JSON or XML format, making it lightweight and easy to use. SOAP, on the other hand, uses XML exclusively and provides built-in error handling and security features. REST is generally better for public APIs and mobile applications where bandwidth might be limited, while SOAP might be preferred for enterprise applications where formal contracts between services and advanced security are essential. I’ve worked with both and find that REST’s simplicity makes it the go-to choice for most modern web applications.
3. What HTTP methods are commonly used in REST APIs and what do they do?
This question tests your knowledge of the fundamental operations in REST APIs. Interviewers want to confirm you understand how different HTTP methods map to different actions on resources, which is central to RESTful design.
In your answer, clearly define each main HTTP method (GET, POST, PUT, DELETE, PATCH) and explain their standard uses. Make sure to highlight the idempotent nature of certain methods, as this shows deeper understanding.
To strengthen your response, briefly mention how these methods relate to CRUD operations in databases. This connection demonstrates your ability to see how REST APIs integrate with backend systems.
Sample Answer: The main HTTP methods used in REST APIs are GET, POST, PUT, PATCH, and DELETE. GET retrieves resources without modifying data. POST creates new resources and isn’t idempotent, meaning multiple identical requests might create multiple resources. PUT updates resources by replacing them completely and is idempotent. PATCH applies partial updates to resources. DELETE removes resources and is also idempotent. These methods map nicely to CRUD operations: GET for Read, POST for Create, PUT/PATCH for Update, and DELETE for Delete. When designing APIs, I always ensure these methods are used consistently to make the API intuitive for other developers.
4. What is idempotence in REST APIs?
Interviewers ask this question to assess your understanding of a key REST concept that affects API reliability and safety. Knowing which operations are idempotent demonstrates your grasp of API design best practices.
Begin your answer with a clear definition of idempotence. Then explain why this property matters in distributed systems where network failures might cause clients to retry operations.
For a standout response, give examples of which HTTP methods are idempotent and which aren’t, and explain how this affects API design decisions. This practical application of the concept shows depth of knowledge.
Sample Answer: Idempotence means that making the same request multiple times has the same effect as making it once. This is crucial for reliability in distributed systems where network issues might cause clients to retry operations. GET, PUT, and DELETE are idempotent methods. For example, if I send the same PUT request to update a user’s profile five times, the end result is the same as sending it once. POST is typically not idempotent since multiple identical POST requests might create multiple resources. In my experience, understanding idempotence helps design more robust APIs by ensuring operations can be safely retried without unexpected side effects.
5. Explain the concept of statelessness in REST APIs.
This question evaluates your understanding of one of REST’s core constraints. Interviewers ask it to check if you grasp how statelessness affects API design and scalability.
In your answer, clearly define what statelessness means in the context of REST APIs. Explain that each request from client to server must contain all information needed to understand and process the request.
To demonstrate deeper knowledge, discuss both the benefits (scalability, reliability) and challenges (increased payload size, authentication complexities) of statelessness. This balanced view shows mature understanding of architectural trade-offs.
Sample Answer: Statelessness in REST APIs means that the server doesn’t store any client context between requests. Each request from a client to the server must contain all the information needed to understand and process that request. This makes REST APIs highly scalable since any server can handle any request without needing to retrieve session information. It also improves reliability because there’s no session state that could be lost. In practice, I implement statelessness by including authentication tokens in each request and designing endpoints to require all necessary parameters rather than relying on stored client state. This approach has its challenges with authentication and sometimes larger request payloads, but the scalability benefits usually outweigh these concerns.
6. What are the different levels of the Richardson Maturity Model for REST APIs?
Interviewers ask this question to gauge your theoretical knowledge of REST API design standards. Your familiarity with this model shows you’re aware of industry best practices and can evaluate API quality.
Start by briefly explaining what the Richardson Maturity Model is. Then clearly outline each level, from Level 0 to Level 3, highlighting the key characteristics of each stage.
For a comprehensive answer, mention how each level builds upon the previous one, creating increasingly “RESTful” APIs. Include your perspective on which level represents true REST according to Fielding’s definition.
Sample Answer: The Richardson Maturity Model describes the path to RESTful API design through four levels. Level 0 is the starting point—using HTTP as a transport mechanism for remote interactions but not leveraging any web mechanisms. Level 1 introduces resources, where we use different URLs to interact with different resources rather than a single endpoint. Level 2 adds HTTP verbs, using standard methods like GET, POST, PUT, and DELETE appropriately. Level 3, the highest level, introduces HATEOAS (Hypermedia as the Engine of Application State), where responses include links that help clients discover what they can do next. Many APIs claim to be RESTful at Level 2, but according to Roy Fielding’s original definition, true REST requires Level 3 with hypermedia controls.
7. What is HATEOAS and why is it important for REST APIs?
This advanced question tests your knowledge of one of REST’s more sophisticated aspects. Interviewers ask it to see if you understand what makes an API truly RESTful according to Fielding’s original definition.
Begin by explaining what HATEOAS stands for and what it means in practice. Focus on how it allows clients to navigate APIs dynamically through links provided in responses.
To show deeper understanding, discuss the practical benefits of HATEOAS, such as reduced coupling between client and server and the ability for APIs to evolve without breaking clients. Include a simple example of how a HATEOAS response might look.
Sample Answer: HATEOAS stands for Hypermedia as the Engine of Application State. It’s the concept that API responses should include links to related resources and available actions. For example, when you request information about a user, the response might include links to their orders, preferences, and actions like “update” or “delete.” This is important because it allows clients to dynamically discover what they can do next instead of hardcoding these relationships. In practice, HATEOAS reduces coupling between clients and servers, making APIs more discoverable and allowing them to evolve without breaking existing clients. While implementing full HATEOAS can be complex, even partial implementation improves API usability and maintenance. I’ve found that including even basic “next action” links helps other developers use APIs more effectively.
8. What are the common HTTP status codes you should use in a REST API?
Interviewers ask this question to assess your knowledge of API communication standards. Proper status code usage indicates professional-level API design skills.
In your answer, group status codes into their major categories (2xx, 3xx, 4xx, 5xx) and explain the general meaning of each group. Then highlight the most common specific codes within each category.
For a comprehensive response, include examples of when to use specific status codes in real API scenarios. This practical application demonstrates that you understand both the theory and implementation of proper HTTP communication.
Sample Answer: HTTP status codes fall into five categories: 1xx for informational responses, 2xx for success, 3xx for redirection, 4xx for client errors, and 5xx for server errors. The most common success codes I use are 200 (OK) for general success, 201 (Created) when a resource is created, and 204 (No Content) for successful operations that don’t return data. For client errors, 400 (Bad Request) indicates invalid syntax, 401 (Unauthorized) means authentication is required, 403 (Forbidden) indicates the client lacks permissions, and 404 (Not Found) means the resource doesn’t exist. For server errors, 500 (Internal Server Error) is the general error, while 503 (Service Unavailable) indicates temporary unavailability. Using appropriate status codes makes APIs more intuitive and helps clients properly handle different scenarios.
9. What is content negotiation in REST APIs?
This question tests your understanding of how REST APIs handle different data formats. Interviewers ask it to see if you know how to build flexible APIs that can serve diverse client needs.
Start your answer by defining content negotiation as the process of selecting the best representation for a response based on the client’s preferences. Explain the mechanisms used for this negotiation, primarily through HTTP headers.
To demonstrate deeper knowledge, discuss both server-driven and agent-driven negotiation approaches. Include examples of relevant HTTP headers like Accept, Content-Type, and Accept-Language and how they’re used in practice.
Sample Answer: Content negotiation is how a client and server agree on the format of the data they exchange. It allows the same API endpoint to return different representations of the same resource based on what the client prefers. This happens primarily through HTTP headers. The client sends an Accept header specifying which media types it can handle (like “application/json” or “application/xml”), and the server responds with the requested format if possible, indicating this with the Content-Type header. Other negotiation aspects include language (Accept-Language), character encoding (Accept-Charset), and compression (Accept-Encoding). In my experience, supporting at least JSON and XML formats makes APIs more accessible to different client types, though most modern APIs default to JSON unless there’s a specific need for alternatives.
10. How would you handle API versioning and why is it important?
Interviewers ask this question to assess your understanding of API lifecycle management. Your answer reveals how you balance evolving API functionality with maintaining backward compatibility.
Begin by explaining why API versioning is necessary—primarily to allow the API to evolve without breaking existing clients. Then describe different versioning strategies with their pros and cons.
For a comprehensive answer, include your recommendation on which approach tends to work best in different circumstances. This shows you can make informed architectural decisions based on project needs.
Sample Answer: API versioning is essential because it allows APIs to evolve while maintaining backward compatibility for existing clients. There are several approaches: URL path versioning (like /api/v1/resources), which is simple and explicit; query parameter versioning (?version=1); custom HTTP headers (X-API-Version: 1); and content negotiation using the Accept header (Accept: application/vnd.company.app-v1+json). Each has trade-offs. URL versioning is highly visible but can lead to duplication. Header-based approaches are cleaner from a RESTful perspective but less discoverable. I typically recommend URL versioning for public APIs due to its clarity, while header-based versioning often works better for internal APIs. Regardless of the method, clear documentation and a consistent deprecation policy are crucial for helping clients transition between versions smoothly.
11. What are the key security considerations for REST APIs?
This question evaluates your awareness of API security issues. Interviewers want to ensure you build APIs that protect both the system and its data.
Start with an overview of the main security concerns for APIs. Then cover essential protection mechanisms like authentication, authorization, input validation, and transport security.
For a standout answer, mention both basic safeguards and more advanced protection strategies. Include real-world examples of how security failures can impact systems to demonstrate the importance of these measures.
Sample Answer: REST API security requires multiple layers of protection. Authentication verifies who is making requests, typically using tokens like JWT or OAuth. Authorization determines what authenticated users can access. Transport security through HTTPS prevents data interception. Input validation guards against injection attacks and malformed requests. Rate limiting prevents abuse and DoS attacks. In my experience, implementing token-based authentication with short expiration times, using HTTPS exclusively, validating all inputs server-side, and applying the principle of least privilege for authorization provides a strong security foundation. I also recommend security headers like Content-Security-Policy and regular security audits. One often overlooked aspect is proper error handling that doesn’t leak sensitive information in error messages.
12. Explain the difference between PUT and PATCH methods.
Interviewers ask this question to test your understanding of HTTP method semantics and appropriate usage. The distinction between these similar methods reveals your attention to REST API design details.
Begin by clearly defining both methods and their standard uses. Emphasize that PUT replaces an entire resource while PATCH applies partial modifications.
To demonstrate deeper knowledge, discuss the idempotence of both methods and give examples of when each would be more appropriate. Include sample request bodies to illustrate the difference concretely.
Sample Answer: PUT and PATCH both update resources, but in different ways. PUT replaces the entire resource with the provided representation. If you send a PUT request with just a name field, any existing email or other fields will be removed. PUT is idempotent—sending the same request multiple times has the same effect as sending it once. PATCH, on the other hand, applies partial modifications to a resource. It only updates the fields specified in the request, leaving others unchanged. For example, a PATCH with just {“name”: “New Name”} would update only the name while preserving all other fields. PATCH is more bandwidth-efficient for small changes but can be more complex to implement correctly. I typically use PUT when clients have the complete resource state and PATCH when they’re updating just a few fields of a larger resource.
13. What is Cross-Origin Resource Sharing (CORS) and why is it important for REST APIs?
This question assesses your understanding of web security mechanisms that affect API usage. Interviewers want to see if you’re aware of browser restrictions and how to work with them.
Start by explaining what CORS is and why it exists as a security feature in browsers. Then describe how it impacts REST APIs, particularly those meant to be called from web applications.
For a comprehensive answer, outline how to implement CORS properly, including the relevant HTTP headers and handling preflight requests. Include common pitfalls and best practices around CORS configuration.
Sample Answer: Cross-Origin Resource Sharing (CORS) is a security feature implemented by browsers that prevents JavaScript from making requests to a different domain than the one serving the web page. It’s important because without CORS, your REST API might be inaccessible to browser-based applications hosted on different domains. CORS works through HTTP headers—the server specifies which origins can access its resources, which HTTP methods are allowed, whether credentials can be included, and how long these permissions can be cached. The key headers are Access-Control-Allow-Origin, Access-Control-Allow-Methods, and Access-Control-Allow-Headers. For requests with certain characteristics (like custom headers), browsers send a “preflight” OPTIONS request to check permissions before sending the actual request. When implementing APIs, I ensure CORS is properly configured for legitimate use cases without being too permissive. A common mistake is using ‘‘ wildcard for Access-Control-Allow-Origin when credentials are required, which browsers don’t allow.*
14. How would you document a REST API?
Interviewers ask this question to gauge your commitment to creating usable, maintainable APIs. Good documentation is essential for API adoption, and your answer reveals how you approach this critical aspect.
Begin by explaining why API documentation is important for both internal and external developers. Then outline the key components that should be included in comprehensive API documentation.
For an impressive answer, discuss both manual and automated documentation approaches. Mention specific tools and standards (like OpenAPI/Swagger) that help create and maintain API documentation.
Sample Answer: Thorough API documentation is essential for adoption and proper usage. I approach documentation with both human readers and automated tools in mind. For structure, I use the OpenAPI Specification (formerly Swagger) to document endpoints, parameters, request bodies, response schemas, authentication requirements, and status codes. This provides both human-readable documentation and machine-readable definitions that can generate client libraries. For each endpoint, I include a clear description of its purpose, example requests and responses, and potential error cases. I find that in-code documentation that generates these specs keeps documentation in sync with the actual implementation. Tools like Swagger UI or ReDoc then present this information in an interactive format. For more complex APIs, I supplement with tutorials and guides that show how to use the API for common scenarios. Good documentation significantly reduces support requests and improves developer experience.
15. What are microservices and how do REST APIs fit into a microservice architecture?
This question tests your understanding of modern architectural patterns. Interviewers want to see if you grasp how APIs function within larger system designs.
Start by defining microservices architecture and its key characteristics. Then explain the role of REST APIs as the communication mechanism between different microservices.
For a comprehensive answer, discuss both the benefits and challenges of using REST APIs in microservices. Touch on alternatives like gRPC or message queues and when they might be more appropriate.
Sample Answer: Microservices architecture breaks applications into small, independent services that focus on specific business functions. Each service can be developed, deployed, and scaled independently. REST APIs play a crucial role in this architecture by providing a standardized way for these services to communicate. They enable loose coupling between services, allowing teams to work independently and choose different technologies as needed. In a typical setup, each microservice exposes a REST API that other services can call. This approach benefits from REST’s simplicity and the stateless nature that supports scalability. However, there are challenges too. Direct synchronous REST calls between services can create dependencies that affect resilience. In my experience, a hybrid approach works best—using REST APIs for query operations and synchronous interactions, while employing message queues for asynchronous processes and event-driven communication. This balances the simplicity of REST with the reliability needed in distributed systems.
Wrapping Up
Getting ready for REST API interview questions takes practice and a solid understanding of the underlying concepts. The questions and sample answers in this guide cover the fundamental principles and practical aspects that interviewers look for in candidates.
As you prepare, focus on understanding not just the “what” but the “why” behind REST API design decisions. This deeper knowledge will help you answer questions confidently and demonstrate your expertise beyond memorized definitions. Good luck with your interview—you’ve got this!